This project studies impossible differential cryptanalysis on substitution-permutation networks.

The code is written in Python 3 and C++.

Run the following commands from the root directory of this project to install the dependencies:

$ pip install -r requirements.txt
$ py.test

Description of SomeCipher and attacks carried out will be uploaded in a report soon.

The source code of SomeCipher is available at some_cipher.cpp. The header file is available at some_cipher.h.

To build the project, simply run make.

Run the following commands from the root directory:

cd find_dist
python3 gen_graph.py # generates graphs of how differentials propagate in a single round
python3 find_ids.py # find 3-round impossible differential properties
python3 create_dist.py > dists.txt # find 6-round distinguishers
python3 find_dist_pairs.py # find pairs of 6-round distinguishers

gen_graph.py will generate the files backward.gpickle, forward.gpickle, rev_backward.gpickle and rev_forward.gpickle. These are graphs of how differentials propagate in a single round. Each edge has a weight, which is the negated logarithmic probability.

The procedure of finding the distinguishers is briefly described in the report.

./gen_bf # generates bf.txt which contains a key, plaintext and ciphertext
cat bf.txt | ./bf 0 1024 # 0 and 1024 are the start and end partitions respectively

Run the following commands from the root directory:

./gen_pairs 256 # generates pairs_256.txt where 256 is the no. of filtered PT-CT pairs
cat pairs_256.txt | ./idc 0 1024 # 0 and 1024 are the start and end partitions respectively

The same applies to launching a double distinguisher attack. To do so, just replace gen_pairs with gen_pairs2 and idc with idc2.